1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device and a method for fabricating the same, and more particularly, to an array substrate having thin film transistors for a liquid crystal display (LCD) device and a method for fabricating the array substrate using flexible materials.
2. Discussion of the Related Art
A liquid crystal display (LCD) device uses optical anisotropy characteristics of liquid crystal molecules to display images. Typical LCD devices include upper and lower substrates with a liquid crystal material interposed therebetween.
FIG. 1 is an exploded perspective view illustrating a typical LCD device. The LCD device includes an upper substrate 9 and a lower substrate 11 opposing each other and a liquid crystal layer 14 interposed therebetween. The upper substrate 9 and the lower substrate 11 are commonly referred to as a color filter substrate and an array substrate, respectively. A substrate 5, a black matrix 6 and a color filter layer 7 that includes a plurality of sub-color-filters red (R), green (G), and blue (B) are formed on the upper substrate 9. The black matrix 6 surrounds each of the sub-color-filters to form an array matrix. Additionally, a common electrode 18 is formed to cover the color filter layer 7 and the black matrix 6 on the upper substrate 9.
The lower substrate 11 includes a plurality of thin film transistors (TFTs) “T” arranged in an array matrix on a substrate 22 corresponding to the color filter layer 7. Each of the TFTs “T” function as switching elements. In addition, a plurality of crossing gate lines 13 and data lines 15 are orthogonally disposed on the lower substrate 11 such that each of the TFTs “T” are located near a corresponding crossing portion of the gate lines 13 and the data lines 15, thereby defining a pixel region “P.” In the pixel region “P,” a pixel electrode 17 is disposed and is made of a transparent conductive material such as indium tin oxide (ITO), for example.
Liquid crystal molecules of the liquid crystal layer 14 are aligned according to electric signals applied by the TFTs “T,” thereby controlling incident rays of light to display an image. Specifically, electrical signals applied to the gate line 13 and the data line 15 are transmitted to a gate electrode and a source electrode of each the TFTs “T,” respectively. The signal applied to the drain electrode is transmitted to the pixel electrode 17, thereby aligning the liquid crystal molecules of the liquid crystal layer 14 in a first direction. Then, light generated from a backlight (not shown in the figure) selectively passes through the liquid crystal layer 14 to display an image.
A fabricating process for the above-described array substrate requires repeated steps of deposition and patterning of various layers. The patterning steps implement photolithographic processing steps, i.e., a masking step, including selective light exposure using a mask, i.e., a photomask. Since one cycle of the photolithographic processing step is facilitated with a single mask, the total number of masks used in the fabrication process is a critical factor in determining the necessary total number of patterning steps. Furthermore, as fabricating processes for the array substrate become more simplified, fabrication errors associated with the fabricating processes may decrease. Moreover, other processing steps such as etching and striping, for example, are also repeated during fabrication of the array substrate.
FIG. 2 is an enlarged plan view illustrating a pixel of a related art array substrate 11 for a liquid crystal display. In the FIG. 2, the array substrate 11 includes a pixel “P” defined by crossing gate and data lines 13 and 15, respectively. The pixel “P” includes a TFT “T” as a switching element, the pixel electrode 17, and a storage capacitor “C.” The TFT “T” includes a gate electrode 26, a source electrode 28, a drain electrode 30, and an active layer 55. The source electrode 28 is electrically connected to the data line 15, and the gate electrode 26 is electrically connected to the gate line 13.
FIG. 3 is a cross sectional view along II-II of FIG. 2, showing a related art array structure resulting from a conventional fabricating sequence. In FIG. 3, a transparent glass substrate 22 is used to form a switching element thereon. The thin film transistor “T” including the gate electrode 26, the source electrode 28 and the drain electrode 30 is formed on the substrate 22. A passivation layer 29 is subsequently formed on the thin film transistor “T” and the pixel electrode 17 that contacts the drain electrode 30 is formed thereon.
In the conventional process described above, mechanical characteristics of the material for the substrate 22, such as that of glass or quartz, are rigid so that the fabrication processes can be done easily due to minimize deformation of the substrate. However, any concentrated point loading, such as an external impact, can fracture the material.